Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client (running SSH server and SSH client programs, respectively).

At the Server

Have a seat and login to the server machine to your account. If this is the root account it’s ok for now but if it’s not I suggest to type these commands:

sudo su
passwd

and set a password in order to be able to login as root from now on. If you did so simply logout (Ctrl-D) and login as root by typing su -

Next we’ll need to create a new user that I suggest to have a strange name. In these article I’ll use the name saint for username. To do so type these commands:

useradd -d /home/saint -m -U -s /bin/bash saint
passwd saint

and set a password for this user. Notice that this user doesn’t belong to sudoers so he can’t execute commands that require root account privileges simply by typing his password but if he wants to do so he must know the root’s password and become root by typing su -

This is how to build an alarm clock using the Linux at command.
It also uses the mplayer command line utility which can/must be installed.

Firstly, we need an mp3 song to be stored in a user’s directory. Let’s assume that it’s the ~/Music/Celesta.mp3 file.
Then, I’ll use the { mplayer -really-quiet ~/Music/Celesta.mp3; } & command so the song be played in the background in its own shell { } and leave space for the next command (notify-send "Wake up" "$(date +%R)\nIt's about time" -i face-wink) to display the notification.